1. Field of the Invention
The present invention relates to a UV (Ultraviolet) curable antireflective coating composition, an antireflective coating film using the same, and its manufacturing method. More particularly, the present invention relates to a UV-curable antireflective coating composition that is cured at a normal temperature in a UV curing manner, an antireflective coating film using the same, and its manufacturing method.
2. Description of the Related Art
Modern persons come in contact with various displays such as Braun tubes like CRT (Cathode-Ray Tube) for monitors and CPT (Color Picture Tube) for TV, TFT-LCD (Thin Film Transistor—Liquid Crystal Display) polarizers, PDP (Plasma Display Panel) filters, RPTS (Rear Projection TV Screen) filters, LCD for cellular phones, watches, photos, and picture frames. When exposed to light, such displays give a reflective light, causing fatigue on the eyes or headache, and also an image is not clearly formed in such displays, resulting in deteriorated contrast.
To solve such problems, a study for forming an antireflective coating film is in progress. In this study, a film having a lower refractive index than a substrate is formed on the substrate to lower reflexibility. This low refractive index film may have a single layer by vacuum deposition of magnesium fluoride (MgF2) with a low refractive index or have multiple layers by laminating films with different refractive indexes. However, the vacuum technique such as vacuum deposition, used for forming a multi-layer film, requires a high cost, so it is not practical.
In this regards, Japanese Laid-open Patent Publication H5-105424 discloses a method for forming a low refractive index film by coating a coating liquid containing MgF2 particles on a substrate by means of wet coating such as spinning or dipping. However, a film obtained by this method has drawbacks of seriously low mechanical strength and very bad adhesive force with the substrate, so it can be hardly used. In addition, this film has a curing temperature over 100° C., so it cannot be used for a plastic substrate made of PET (polyethylene terephthalate), PC (polycarbonate) or TAC (tri-acetyl-cellulose).
Meanwhile, to solve the drawbacks of the above method using a coating liquid containing MgF2 particles, there are proposed other methods in Japanese Laid-open Patent Publication 1997-208898, Japanese Laid-open Patent Publication 1996-122501 and so on. These documents disclose a method for making a coating liquid with a low reflection function and a stain resistance function according to a lowered surface energy by using a compound having fluoric silane and fluoric alkyl group. However, the low reflection layer containing fluoric silane is easily electrically charged due to friction or the like by the fluoric group positioned on the film surface, so dust is easily adhered thereto, and the dust is not easily detached once it is adhered thereto. Also, this method adopts heat curing, which needs a high curing temperature or a long curing time disadvantageously.
These problems may be solved if good mechanical strength, good adhesion to the substrate and low curing temperature are satisfied using UV-curable materials and a coating liquid containing metal fluoride particles with a refractive index of 1.40 or less. However, a metal fluoride particle with a refractive index of 1.40 or less is generally coated by means of wet coating, not using a single deposition manner, so its mechanical strength and adhesion to the substrate are deteriorated when forming a low refractive index film. Also, such a metal fluoride particle needs a high curing temperature. In addition, when being used together with UV-curable materials such as acrylate as well as other heat-curing materials such as silane, the metal fluoride particle shows a problem in compatibility, namely easily settling down or becoming misty when forming a film, so it can be hardly used.
As mentioned above, there have been many endeavors for making an antireflective coating film having excellent mechanical strength, improved adhesion to a substrate, a shortened heat curing time and a prevention of dust attachment by progressing a UV curing process using metal fluoride particles with a refractive index of 1.40 or less, photopolymerizable monomer and photopolymerization initiator, and the present invention is designed under such circumstances.